In the industry of optical disc drives, optical drives are enhanced from the early developed read-only optical disc drives, e.g. CD-ROM drives or DVD-ROM drives, to the present recordable optical disc drives, e.g. CD-RW drives, DVD-RW drives and DVD+RW drives. As known, the tracks of a recordable disc to be written by the recordable optical drives have wobble marks, such that a wobble signal can be obtained by decoding the wobble marks, thereby positioning absolute positions where data are to be written.
Generally, the recordable disc drive writes data into the optical disc from inner tracks to outer tracks. Therefore, when the quantity of data written into the recordable disc drive is not large enough to fill all tracks of the optical disc, there would be blank in the outer track area of the optical disc. Data may subsequently be written into the blank area at one or more times until the optical disc is finalized by the recordable disc drive to refuse further data.
An optical disc with blank area has no problem being accessed by a recordable disc drive, regardless of the possible focusing location of an optical pickup head in the blank area. In contrast, if a read-only optical disc drive is used to access the optical disc with blank area, the optical pickup head has to focus on a track in the data area other than in the blank area. It is because the servo control system of the read-only optical disc drive cannot generate any wobble signal and track cross signal, and thus a track-on operation cannot be performed in the blank area. Accordingly, the servo control system of the read-only optical disc drive would fail if the optical pickup head focuses on a track in the blank area. Once the servo control system fails, it would take a long time for the read-only optical disc drive to recover to work, so the performance of the read-only optical disc drive is adversely affected.
Currently, one of the most popular applications of a read-only optical disc drive is the use in a player system, e.g. a DVD player. In the player system, if a track-on operation of an optical disc cannot be successfully executed due to the presence of blank area, the optical disc will still be deemed invalid, which often bothers the user very much. Therefore, a variety of prior art has tried to solve the problem.
For example, U.S. Pat. Pub. No. 2004/0057365 entitled “method and apparatus for detecting the blank region of the optical storage medium” proposes a solution to the problem. Referring to FIG. 1, the detecting apparatus includes a waveform detection module 52, a programmable gain amplifier 56, a selective gain boost module 54, and a blank region judgment module 58. The blank region judgment module 58 further includes a slicing comparator 59 and a high/low (H/L) pulse detector 60. According to the detecting apparatus, whether the focusing location of the optical pickup head is in the data area or the blank area is determined by selectively amplifying the 3 T˜11 T frequency of the radio frequency (RF) signal and comparing it with a preset reference level.
U.S. Pat. No. 6,728,180 entitled “Blank detection circuit and method therefore” proposes another solution to the problem. As illustrated in FIG. 2, the blank detection circuit includes an analog/digital converter (ADC) 102, edge detector 104, maximum/minimum value detector 106, determiner 108, and blank signal generator 110. An RF signal generated by an optical pickup head is converted into a digital RF signal by the analog/digital converter 102. Then the edge detector 104 and the maximum/minimum value detector 106 determine the interval between the detected edges of the digital RF signal and the amplitude of the digital RF signal. The determiner 108 determines whether or not the optical pickup head is being situated in blank area of the optical disc according to the determined interval and amplitude. If it is, the blank signal generator outputs a blank signal.
As described above, the prior art blank area detection methods are determined with RF signals, e.g. depending on whether the amplitude of the RF signal exceeds a preset reference level or whether the RF signal contains a valid data length (3 T˜11 T). If not, the location in the blank area is determined. However, if the reflective rate of the detected optical disc is higher or lower than that generalized in the specification, the amplitude of the resulting RF signal may become higher or lower than usual. Under this circumstance, the comparison of the amplitude with the preset reference level is indefinite and thus the detecting result becomes unreliable.